Hi - sounds like you needed an impact screw driver set at the begining. Too late now for the ones that are damaged.

An impact screw driver has a tip that fits the slot of the screw, and then you hit the end of the impact area with a hammer.
It vibrates the screw loose, and at the same time applies a twisting motion.
In Australia, about $20 at any good tool shop for a cheap set.

Good luck

PK